Item disappeared during “Return to Sender”

Hi all, looking to see if this has happened to anyone else here.

I sold a designer item a couple of weeks ago on depop and promptly used the depop-provided pre-paid shipping label to send it via USPS. Once the item arrived to the buyer, they claimed that the postman was asking them for an additional $12.99 in fees at their doorstep, so they declined the delivery and asked that it be returned to the sender. They also began relentlessly messaging me asking why I was requesting more money (I wasn’t) and gave my shop a 1 star review, but that’s a separate issue. Anyway, the tracking shows that delivery was refused and that the item is “on the way back to me” but it hasn’t moved in over 2 weeks.

I contacted depop and asked that I be reimbursed for this “lost” item, I’ve also contacted USPS as the package was insured (and expensive!!). I believe that I will likely get some $ for this item, but I’m frustrated by this situation as it feels like some sort of scam? I’ve never had any issues with selling items on depop in the past, and I’ve sold a lot. I don’t know why the buyer would claim that more money was requested at their doorstep, nor do I understand how the item disappeared after that.

Has anyone had something like this happen to them before? TIA